Preheat your oven to 180°C (350°F) for a conventional oven or 160°C (320°F) if using a fan-forced setting. Grease and line two 8-inch round cake tins with baking or parchment paper. In a large bowl, sift together the flour, cocoa powder, baking powder, and baking soda. Add both sugars and whisk everything together. In a separate bowl, combine the buttermilk, vegetable oil, vanilla extract, and eggs, whisking until well mixed. Boil water and measure out 1 cup of hot water. Add the wet ingredients to the dry ingredients, folding gently as you slowly pour in the hot water. Continue mixing until the batter is fully combined. Divide the batter evenly between the two prepared tins and bake for about 30 minutes, or until a skewer inserted into the center comes out clean. Let the cakes rest for 10 minutes before carefully removing them from the tins, then transfer to a wire rack to cool completely.

To prepare the mint buttercream frosting, place the butter in a large mixing bowl and beat with an electric mixer until pale and creamy. Gradually sift in the icing sugar, adding it one cup at a time. Add one or two tablespoons of milk to loosen the mixture as needed. Stir in the peppermint extract and continue beating until smooth. If necessary, add a bit more milk to reach a creamy but thick consistency. Fold in the grated chocolate flecks gently. To frost the cake, level the cake layers if desired using a cake leveler. Place one layer on a cake turntable set on a disposable board for easy handling. Spread a generous layer of frosting on top, then place the second cake layer on top. Cover the entire cake—top and sides—with frosting. Use a cake scraper to smooth the sides or remove excess frosting if you want a rustic “naked cake” look. Chill the cake in the refrigerator for about 30 minutes to firm up the frosting. Reserve any leftover frosting for decorating.

For the ganache, finely chop the dark chocolate and place it in a heatproof bowl. In a small saucepan, heat the cream over medium heat until it begins to simmer, just before boiling. Pour the hot cream over the chopped chocolate, cover the bowl with a plate, and let it sit for 3 to 5 minutes. Whisk the mixture until it becomes smooth and creamy. Refrigerate the ganache for about 30 minutes to allow it to thicken slightly.

To decorate the cake, gently pour the cooled ganache over the top, using a small spatula to encourage drips down the sides. Let the ganache set for a short while. Before serving, pipe dollops of mint buttercream onto the top of the cake using a disposable piping bag fitted with a large star tip. Garnish with mint chocolate cookies and chocolate sprinkles. Enjoy!